Cellular communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
A cellular multiple-access communications system may include a number of base stations, each simultaneously supporting communication for multiple mobile devices. Many mobile devices maintain databases of information used to identify and connect to cellular systems. For example, a mobile device may store a Most Recently Used (MRU) database and a Preferred Roaming List (PRL) database. The MRU database may store identification and connection information (e.g., identifiers, bands, etc.) for a fixed number of cellular systems on which the mobile device most recently camped. The PRL database may store a prioritized list of cellular systems for various service providers, including roaming service providers, and information for discovering and connecting to each stored service provider.
When the mobile device searches for a cellular system (e.g., upon powering up, moving into a new area, etc.), the mobile device may populate a scan list according to the prioritized order of entries in the MRU database, to determine whether any of the cellular systems identified in the MRU database are available. If the mobile device finds that one of the systems specified in the MRU database is available, the mobile device may connect to and camp on that system. If none of the systems specified in the MRU database are available, the mobile device may scan entries from the PRL database appearing in the scan list, which entries are typically greater in number than the entries in the MRU database. It can therefore take longer to connect to a cellular system when a mobile device has to scan entries corresponding to the PRL database.